We analysed concentrations of phenols and key macro-nutrients in a dominant mat-forming lichen, Cladina stellaris, in dry heath forests subjected to heavy reindeer grazing in Finnish Lapland. Lichen samples were collected in the beginning of two growth seasons from six to eight sites with old reindeer exclosures that served as control plots within sites. The concentration of perlatolic acid in lichen apices (top 10 mm) was higher in grazed plots than in control ones, whereas usnic acid did not seem to respond unequivocally to grazing. Moreover, there was a strong negative relationship between nitrogen and phenolic content of Cladina stellaris in intact plots but this relationship was absent in grazed ones. Changes in nitrogen and phosphorus contents caused by reindeer grazing were not correlated with changes in the level of phenolics in lichen thalli. The present result demonstrated that the carbon-nutrient balance (CNB) hypothesis may well explain some of the variation in lichen phenolic content but is not sufficient for explaining changes caused by reindeer grazing. We hypothesized that physical changes in the lichen microenvironment induced by reindeer have more profound impact on lichen phenolic content than alterations in thallus nutrient content.